They are pretty rare. Diaon was a fairly low production Japanese company of the early-mid 80's. Wood working is good quality, hardware OK, pickups are either extremely bright or very thin, depending on how you look at it. Bridge is the same as used on the neck-through Washburn's of the same era. Pickups sound about the same, also.

I actually had a fretless version that I bought new in '83? IMO it was a very nice guitar.It had a smooth playing neck.I would put copperwounds on it and it would sing.But I traded it straight up for a '76 4001 and never looked back.

I have owned one of these for about 20 years. Beautiful instrument; mine looks even nicer than that one.
The Power Mark XX was Daion's "top of the line". Well made. Very nice wood working; bright sounding, as previously stated. Brass hardware and brass tuning fork shaped inlay on the headstock. Plays effortlessly.
As for rarity, I have never seen another one except for pictures on the internet.

As rare as these are (I have only seen a handfull over the years other then mine), when I have seen them for sale they seem to go for in the $500 range. Much more then that would be overpriced, in my opinion.

i have one too. my only complaint is the bridge pick-up. so i only use it with the p pickup. i also run mine through a sadowsky pre. its my only fretted 4 that sees any playtime. i payed like 350 for mine and have been offered 3 or 4 times that for it. just like it too much